[KLIB][tests] Reorganize "klib dump-metadata" tests

- Keep the test data under "native/native.tests/testData/klib/" dir
- Rename tests from "klib contents" to "klib dump-metadata"

native/native.tests/testData/klib/dump-metadata/builtinsSerializer/annotationArguments/varargs.txt

@@ -0,0 +1,9 @@
+    enum class My private constructor() : Enum<My> {
+        enum entry ALPHA
+        enum entry BETA
+        enum entry OMEGA
+    }
+    annotation class ann constructor(vararg m: My) : Annotation {
+        val m: Array<out My>
+    }
+    @ann(m = {My.ALPHA, My.BETA}) annotation class annotated constructor() : Annotation